JPS6021464B2 - X-ray tube and X-ray fluorescence analyzer that can see it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray tube having an emission window and comprising an diaphragm housing a cathode and an anode for generating an X-ray beam.

The present invention also relates to an X-ray detector and optical analysis device using such an X-ray tube. An X-ray source of this type is known from GB 1225405.

The X-ray tube described in this British patent has a relatively thin window, preferably made of beryllium. In these X-ray tubes, for electron and X-ray incidence on the window,
Window material heats up intensely. If the window is made thicker to achieve an adequate service life, a significant portion of the soft x-rays will be absorbed and the x-ray tube will therefore be inefficient for this radiation range. The X-ray tubes described above include a magnetic deflection mechanism that serves to deflect the secondary electrons reflected from and emitted by the anode, so that they do not reach the emission window. However, this type of magnetic shielding system is relatively expensive and requires considerable space near the window. This space is not normally available. Furthermore, this type of shielding is not effective against X-rays. US Patent No. 35,341 discloses an X-ray tube with two optional windows.

For this purpose, the window can be moved relative to the anode by means of a Jiyabara connection. Such a movement mechanism is relatively complex and does not provide additional protection of the radiation window for each position. It is an object of the present invention to provide an X-ray tube which allows measurements to be made over a wide wavelength range without the need for window adjustment and which does not cause excessive heating of the window material.

The inventive X-ray tube is characterized in that the emission window has a non-uniform radiation transmission measured across its surface.

As a result of the non-uniform transmission of the emission window, the inventive X-ray tube has a high radiation efficiency over a wide wavelength spectrum.

This is because relatively soft radiation passes through the thin window, and hard radiation passes through the thick window. In a preferred embodiment of the invention, the emission window is constructed by a window plate having a non-uniform thickness.

In another preferred embodiment, the emission window comprises a stack of two window plates, each of the two window plates having a uniform thickness and the thin window plate providing a vacuum seal for the x-ray tube. The thick window plate extends over a portion of the window opening.The relatively thick window portion is provided in the portion of the window opening that is remote from the anode target when viewed within the x-ray tube. In X-ray beams and optical devices equipped with an X-ray tube, in order to achieve as uniform a radiation of the specimen to be examined as possible,
Install a thick window inside the window closure.

This is done by placing a thick window plate in the area where the window is located relatively close to the specimen. A preferred embodiment of the X-ray tube of the present invention will be described in detail based on the drawings.

FIG. 1 shows an x-ray fluorescence analysis tube according to the invention.

This X-ray tube includes a glass envelope 1, and a holder 2 is provided around the envelope. This holder in this case surrounds the oil space 3 and comprises an entry □4 for the high-voltage plug and a filament connection for the cathode 5 provided in the housing. The cathode comprises an emitter element 6 which can be heated via a supply IJ-wire 7 connected to a contact pin 8. A shielding sleeve 9 is provided around the cathode. The emitter element can be formed as a filament coil, but it can also be formed as a private heating element as described in US Pat. No. 3,497,757. In the X-ray tube according to the present invention, since a small anode target point and a high current density of the electron beam are required, an electron emitting material such as barium oxide is applied to the anode by means of a porous force bar plate suitably impregnated with osmium. It is particularly effective to use storage cathodes which are contained in closed spaces on opposite sides. Therefore, both a relatively high emission current density and a long service life can be obtained without causing evaporation or sputtering of the cathode material. Furthermore, the electron optical system within the X-ray tube can be optimized by making the shape of the cathode and its emitting surface more precise. On the opposite side of the cathode, the cathode sleeve 1
Set 0. The cylindrical portion 12 of this anode sleeve extends far from the vicinity of the cathode. One end of the anode sleeve opposite the cathode is closed by an anode body 14 . An anode target 16 is provided on this anode body. The anode can be cooled by a liquid circulation duct 17.

The anode target can form part of the anode body, for example made of copper, but it can also be provided as a separate plate on or within the anode body. Targets of this type can be used, for example, according to the desired radiation: ``tungsten, chromium, molybdenum,
Made of silver, gold or rhodium. In the above-mentioned X-ray tube, the soft La
The anode target is made of rhodium, which can generate radiation and anti-Ka radiation. As a result, this X-ray tube is suitable for the analysis of elements with significantly different atomic numbers. Yet another advantage is that rhodium itself is rarely present in the specimens analyzed. A radiation opening 18 is provided in the anode sleeve in the vicinity of the anode target, which is closed by a window 201.

In known X-ray tubes, the window has a diameter of about 15 skins and a thickness of 0.25 to 1.0 ribs, depending on the hardness of the radiation produced. According to the invention, the windows have non-uniform thickness, as shown for example in the preferred embodiment of FIG. The window gate 18 is hermetically sealed with three beryllium discs. This window plate can be provided in the window gateway by means of a sealing diffusion ring 32. This beryllium disk has a thickness of, for example, 0.15 ribs and a diameter of, for example, 15 sides. A second beryllium plate 34 is provided in the window opening via the ring 33. This disk has a semicircular shape and is provided on the side of the window closure at a position far from the anode target. This second window plate is provided on the inside of the sealing window plate 30. In this case, the second window plate is made of beryllium and has a thickness of, for example, 0.5 to 1. The thickness can be adapted to the absorption of these materials: a portion 36 of the X-ray beam generated by the electron beam 35 passes through the thick window section and a portion 37 through the thin window section. In the case of radiation, only the thin window part almost acts as a radiation window, and in the case of hard radiation, the entire window acts as a radiation window.The electrons reflected by the emitted target point are Due to the shape of the target, it mainly moves towards the thick window plate and is blocked by this window plate.

Because the window plate is thick, the heat generated within the plate can be dissipated more easily, and since the plate has no vacuum sealing function, a high degree of destruction is tolerated. Further improvements in this respect can be achieved if the window plate 34 is made completely or partially of a material with good thermal conductivity or a large heat capacity. Furthermore, to improve the tightness, the thin window plate can be made of beryllium coated with titanium. A titanium coating of several microns provides excellent airtightness. The window plate 34 can also be formed to have different shapes, such as a hook shape, or a plate can be utilized that extends completely around the circumference and has inlets in the area of the desired thin window.

Heat dissipation to the window frame can be improved by such a shape. Yet another preferred embodiment window is comprised of a single plate in which the thin section can be achieved by localized removal of the window plate material.

This embodiment is particularly suitable for window plates formed by splicing of window plate material. The reason for this is that a mold having a desired shape can be used between the molds. Thick and thin window plate sections can be alternated if necessary, and it is relatively easy to form a window plate with a ring of uniform thickness around the entire circumference for installation in a window gateway. It's easy. In order to reduce the occurrence of scattered radiation in the x-ray beam from the x-ray tube, it is preferred to cover the anode sleeve and possibly associated parts of the anode body with a optical material such as aluminum.

These portions are also included in the Tokuto Sho 5 related to the applicant's other applications.
It can be made from the materials listed in 3 Seal 483M (Tokukan Sho 53-1133387) "X-ray tube". An X-ray tube 40 having an emission window and comprising an external device accommodating a cathode and an anode for generating an X-ray beam, a specimen holder 41 holding a specimen 49 to be examined, and a first collimator 42 In the X-ray optical analyzer of the present invention, which includes an analysis crystal 43, a second collimator 44, and a detection device 45, the emission windows 20, 48 of the X-ray tube 40
has a non-uniform radiation transmission measured across its surface and a relatively thin window portion, the distance between the anode and the specimen to be irradiated is relatively large, through which the radiation passes. It is characterized by being placed in the inner area.

The optical device is an X-ray tube 4 shown diagrammatically in FIG.
0 (in this case shown in cross section through the radiation window), the specimen holder 41, the first collimator 42, and the analytical crystal turtle 3.
, a second collimator 44 , and a detection device 45 .

The X-ray beam 471 generated from the anode target point 46 passes through the radiation window 48 and is transmitted to the specimen 4 placed on the specimen holder 41.
9. The distance between the specimen and the anode target point is not uniform when measured across the specimen. In order to make the irradiation area of the specimen as uniform as possible,
Preferably, a relatively thick window section is provided in the region through which the radiation achieves the shortest distance of the specimen. In this example, the thickness also indicates the window plate 50 in the fitted position. The resolution of such an X-ray optical analyzer is advantageously influenced by reducing the anode target point in at least one direction.

Such a reduction cannot be achieved by reducing the radiation intensity, so the current density of the electron beam must be relatively large. Therefore, it is preferable to use an indirectly heated cathode. Since the electron target point is small, the interlocking influence of the electron target point across the anode is further hindered.

External magnetic fields, such as the earth's magnetic field and fields generated by electric motors or the specimen to be measured, cause such displacements. In a preferred embodiment of the invention, the cathode sleeve 9 and/or the anode sleeve 10 contain ferromagnetic material to provide shielding from these magnetic fields. By providing a ferromagnetic material around the electron beam, a particularly favorable stationary electron target point can be achieved.

In this way, maximum benefits can be obtained from the improved window structure. In summary, in the present invention, in the X-ray tube for fluorescence analysis, the window port is sealed by a window having a non-uniform thickness.

The thick window portion is placed on one side of the window closure at a distance from the anode and partially overlaps the thin window plate. In the analyzer, a thick window section is placed in the region of the window through which the radiation passes, where the distance between the anode and the specimen is relatively small. A simple explanation of the drawings. Figure 1 is a diagram showing an x line and an optical analysis tube based on the present invention.
FIG. 2 is a detailed view of the emission window of the X-ray tube, and FIG. 3 is a diagram showing an X-ray marker and optical analyzer equipped with the X-ray tube according to the invention.

1...Glass enclosure, 5...Cathode, 6...'Emitting element, 9...
Shielding sleeve, 10... Anode sleeve, 14... Anode body, 16... Anode target, 18... Radiation port,
20...48...Emission window, 30...Beryllium disk, 34...Second beryllium plate, 35...Electron beam, 36,47...
X-ray beam, 4Q...X-ray tube, 41...specimen holder, 42,
44... Collimator, 43... Analysis crystal, 45...
Detection device, 46...Anode target point.

F Lid 9-Turtle Fig. 2 F Tomi 9-3

Claims (1)

[Claims] 1. An X-ray tube provided with an emission window and comprising an envelope housing a cathode and an anode for generating an X-ray beam,
An X-ray tube, characterized in that the emission window has a non-uniform radiation transmission measured across its surface. 2. The X-ray tube according to claim 1, wherein the radiation window is constituted by a plurality of partially overlapping windows made of a plate of window material. 3. The X-ray tube according to claim 1, wherein the radiation window is constructed from a plate of window material having a non-uniform thickness. 4. The X-ray tube according to claim 1, wherein the relatively thin portion of the radiation window is at least approximately circular. 5. The X-ray tube according to any one of claims 1 to 4, characterized in that a relatively thin portion of the radiation window is disposed in a part of the window opening facing the anode. 6. The X-ray tube according to any one of claims 1 to 5, characterized in that a shielding sleeve between the cathode and the anode includes a ferromagnetic material. 7. The X-ray tube according to any one of claims 1 to 6, wherein the cathode is configured as an indirectly heated cathode. 8. An X-ray tube 40 provided with an emission window and provided with an envelope housing a cathode and an anode for generating an X-ray beam, a specimen holder 41 holding a specimen 49 to be examined, and a first collimator. 42, an analysis crystal 43, a second collimator 44, and a detection device 45.
has a non-uniform radiation transmittance measured across its surface and a relatively thin window portion through which radiation passes through which the distance between the anode and the specimen to be irradiated is relatively large. An X-ray fluorescence analysis device characterized in that it is arranged in an area within an aperture.